With reference to FIG. 1, cable TV (CATV) networks have utilized legacy set-top boxes (STB's) 11 for many years. Such set-top boxes are coupled via a coaxial cable to a headend 12 for cable TV service. Legacy cable telephony 13 sets can also be coupled to the cable network for information exchange.
Cable modems 10 are being deployed today that allow high-speed Internet access in the home over a cable network, often referred to as a Hybrid Fiber/Coax (HFC) cable network. The architecture of a cable modem used in a cable network is shown in FIG. 1. Cable modems (CM) 10 are units that are installed as consumer premises equipment (CPE) that may comprise a personal computer (PC) or other computing device, for example. A cable modem 10 is adapted to communicate with the cable modem termination system (CMTS) that is typically located at a cable network service provider's headend 12. The cable modem 10 is a modulator/demodulator that receives Internet traffic or information, data, TV signals, and telephony from a server through the CMTS and puts it into a format recognizable by a user's PC, allowing a user to browse the Internet, and send/receive e-mail just as they would with a conventional modem on a PC. A cable modem 10 may include a Media Access Control (MAC) layer, a data link layer, and may include network layers. Using a cable modem 10 over a cable network provides a much faster connection, being at least 50 times faster than a 56K modem, for example.
A cable modem 10 performs modulation and demodulation, and the operations necessary to interface with a PC. A cable modem 10 typically comprises a transmitter 14 for upstream modulation of a data signal, usually in short bursts, to a receiver 16 in the headend 12 that serves as an upstream demodulator. The upstream direction refers to sending a data signal from the user at the cable modem 10 towards the headend 12. The upstream signal may comprise TV channel requests, program selection or Internet data request information and telephony signals, for example, and may be a QPSK/16-QAM modulation format at 3 Mbits/s. Cable modem 10 also comprises a receiver 18 for downstream demodulation of signals received from a transmitter 20 in the headend 12 that serves as a downstream modulator. The downstream direction refers to sending a data signal from the headend 12 to the cable modem 10. The downstream modulation/demodulation may be 64-QAM/256 QAM modulation format at 27-56 Mbits/s, depending on the bandwidth, for example. Both the cable modem 10 and headend 12 include MAC functionality, not shown, that control the MAC sublayer of the communication network.
A recent development in cable TV network is the addition of a fiber node 30 coupled between the central office headend 12 and the cable modems 10 in users' homes, as shown in FIG. 1. The fiber node 30 may comprise a fiber node such as AT&T's mini fiber node (mFN) and may be adapted to service around fifty homes or users. A fiber node 30 increases network capacity and reliability, and reduces operating costs, by reducing active components on the final coaxial run to the home.
A problem with using a fiber node 30 in a cable network is that a lot of bandwidth is required. Bandwidth for set-top boxes 11 must be assigned, even though there may be silence on many of the frequencies for the STBs 11.